Influence of subtle inherited basement structures on thin-skinned thrust systems: The Caledonian Thrust Front in Lapland (CaTFLap)

Thin-skinned fold-thrust belts are defined by an extensive detachment surface, “the sole thrust’. The sole thrust is typically assumed to be sub-planar beneath the fold-thrust belt. The model of a planar sole thrust and, by inference, planar basement is often applied rather uncritically, whereas experimental and field studies show that basement topography is not only varied but crucial for the geometrical and kinematic evolution of fold-thrust belts. Basement topography controls on the thrust dynamics remains the least well understood parameter in fold-thrust belts, and more case studies are needed to underpin further understanding. We present field evidence from the well-exposed Caledonian Thrust Front in Lapland, showing the influence of inherited, orogen-perpendicular basement structures on the subsequent structural evolution of the Caledonian sole thrust and its underlying sedimentary rocks. Inherited orogen-perpendicular basement structures created open corrugations in the foreland that directed thrust allochthons and controlled the geometry and strain state of the sole thrust and associated rocks. We propose that even relatively small-scale structures can have a significant control on the geometry and strain state of an evolving thrust system, and that variations in thrust geometries are not simply explained by inversion or coincidental heterogeneous internal thickening (imbrication) of thrust-related units.